The blood coagulation cascade involves a series of serine protease enzymes (zymogens) and protein cofactors. When required, an inactive zymogen precursor is converted into the active form, which consequently converts the next enzyme in the cascade. It is divided into three distinct segments: the intrinsic (contact activation), extrinsic (tissue factor), and common pathways.
In the intrinsic pathway of the cascade, hemophilia is the most pronounced bleeding disorder, which results in insufficient generation of factor Xa by factor FIX (FIXa)/factor VIIIa (FVIIIa) complex (the intrinsic tenase complex) leading to an insufficient clot formation. Bleeding may then occur spontaneously or following injury.
Hemophilia is an inherited bleeding disorder and two forms of hemophilia, hemophilia A and B, are known. Hemophilia A is the consequence of a deficiency of FVIII and is characterized by hemorrhage into the joints and muscles. FVIII circulates in plasma at a very low concentration and is bound non-covalently to von Willebrand factor (vWF). During hemostasis, FVIII is activated by thrombin, separates from vWF and acts as a cofactor for activated FIXa-mediated FX activation by enhancing the rate of activation.
Patients with less than 1% normal FVIII are considered to have severe hemophilia, with 1-5% moderately severe hemophilia, and with more than 5% but less than 40% mild hemophilia.
Nowadays the treatment of choice for the management of hemophilia A is replacement therapy with various plasma derived or recombinant FVIII concentrates. Although specific viral-inactivation steps, including solvent-detergent treatment or liquid-phase heat treatment, are available to inactivate viruses, possible transmission of poorly characterized agents (e.g. prions) in plasma derived concentrates is still an issue discussed in the art.
FVIII is also synthesized as a recombinant protein for therapeutic use in bleeding disorders. Such products have lowered the risk of viral contamination. There are many recombinant products on the market for the treatment of hemophilia A. One of these concentrates is the Advate® FVIII composition, which is produced in CHO-cells and manufactured by Baxter Healthcare Corporation. No human or animal plasma proteins are added in the cell culture process, purification, or final formulation of this product.
Although progress in the production of FVIII to ensure purity, efficacy and viral safety has been made over the past decades, some limitations remain. First of all, severe hemophilia A patients are frequently affected by anti-FVIII inhibitor antibody formation, rendering the therapy ineffective.
Approximately 30% of patients with severe HA develop alloantibody inhibitors that can neutralize FVIII (Hay, Haemophilia 2006; 12 Suppl 6:23-9; Peerlinck and Hermans, Haemophilia 2006; 12:579-90). These inhibitors are typically immunoglobulin G (IgG), predominantly of the IgG4 subclass, that do not fix complement and do not result in the end-organ damage observed with circulating immune complexes. The inhibitors occur at a young age (about 50% by 10 years), principally in patients with less than 1% FVIII. Furthermore, acquired hemophilia may occur, which is the development of FVIII antibody inhibitors in persons without a history of FVIII deficiency. This condition can be idiopathic (occurring in people >50 years), it can be associated with collagen vascular disease or the peripartum period, or it may represent a drug reaction (e.g., to penicillin). For clinical purposes, the magnitude of the antibody response can be quantified through the performance of a functional inhibitor assay from which the Bethesda unit (BU) inhibitor titer can be obtained. The International Society of Thrombosis and Haemostasis (ISTH) definition of a high titer response is >5 BUs and its definition of a low titer response is between 0.5 and 5 BUs.
Attempts to overwhelm the inhibitors with large doses of human FVIII have been tried. Also porcine FVIII, which has low cross-reactivity with human FVIII antibody, has been administered. More frequently, FVIII-bypassing agents, including activated prothrombin complex concentrates (e.g. FEIBA (Factor Eight Inhibitor Bypassing Agent) and recombinant activated factor FVII (FVIIa) have also been used.
Because therapeutic polypeptide drugs such as FVIII are also rapidly degraded by proteolytic enzymes in addition to the drawback of inhibitor development, FVIII needs to be frequently administered intravenously. Taking into account the average half-lives of the various FVIII products in the circulation, this can usually be achieved by giving FVIII two to three times a week. Thus this treatment is rather complicated for an outpatient population, especially in small children.
Thus currently the aim of many manufacturers of FVIII is to develop a next generation product with enhanced pharmacodynamic and pharmacokinetic properties, while maintaining all other product characteristics. Because improved polypeptide drugs with a longer circulation half-life would decrease the number of necessary administrations, chemical or enzymatic modification of the polypeptide drugs is one of the preferred approaches to achieve this goal.
One such example is PEGylation of polypeptide drugs protecting and improving their pharmacodynamic and pharmacokinetic profiles (Harris and Chess, Nat Rev Drug Discov. 2003; 2:214-21). U.S. Pat. No. 6,037,452 describes a poly(alkylene oxide)-FVIII or FIX conjugate, where the protein is covalently bound to a poly(alkylene oxide) through carbonyl groups of said FVIII.
Even if these methods reduce inhibitor development they still would not abrogate the need for intravenous administration. The most elegant option, making most of the drawbacks of hemophilia treatment discussed above obsolete, would be the development of a low molecular weight compound such as a peptide (peptidomimetic) with the capacity to improve coagulation and which can be administered by a non-intravenous route. Though already discussed for many years (for example Kaufman and Pipe, Haemophilia 1998; 4.370-9; Llung, Thromb Haemost. 1999; 82:525-30) no such agent is currently available or in clinical development.
The current state of the art for the use of small peptides in blood coagulation is documented for example by the following publications:
D K Liles, D M Monroe and H R Roberts (1997) Blood Vol 90 No 10 Supplement 1, 463a is a poster abstract disclosing a peptide 698-712 from FVIII which can promote FIXa mediated activation of FX on a phospholipid surface. However, in the presence of FVIIIa, the peptide inhibits FIXa mediated activation of FX on a phospholipid surface. To date, there has been no peer-reviewed publication by these authors confirming results disclosed in this poster abstract.
Blostein et al (2000) Biochemistry 39:12000-12006 discloses that amphipathic alpha helices can interact with FIXa Gla domains and increases activation of FX in the absence of phospholipid. The peptides appeared to work independently of amino acid sequence by mimicking phospholipids. There is no suggestion to use such peptides in therapy. Under normal conditions, activated platelets provide the lipid [0]surface supporting coagulation. Since platelets are activated by thrombin, which is formed at sites of vascular injury, coagulation processes are restricted to the sites of injuries. It is highly undesirable to provide the body with peptides that are general substitutes for procoagulant lipids as this would cause systemic coagulation and ultimately lead to disseminated intravascular coagulation (DIC). Therefore, the peptides described by Blostein would not be useful in therapy.
U.S. Pat. Nos. 7,109,170 and 6,624,289 disclose regions of the FIXa protease domain that interact with FVIIIa. The peptides comprise the FVIIIa binding site of FIXa and inhibit binding of FIXa to FVIIIa. However, they are only useful as anticoagulants for preventing or treating thrombosis.
US20010014456A1 discloses binding molecules for human FVIII and FVIII-like proteins. These polypeptides bind FVIII and/or FVIII-like polypeptides and are useful for the detection and purification of human FVIII and/or FVIII-like polypeptides from solutions such as blood or conditioned media.
In U.S. Pat. No. 7,033,590 FIX/FIXa activating antibodies and antibody derivatives are used for increasing the amidolytic activity of FIXa, and for treating blood coagulation disorders such as hemophilia A and hemorrhagic diathesis.
In U.S. Pat. No. 7,084,109 FVIIa antagonists are disclosed. These antagonists are peptides that inhibit FVIIa activity and are said to be useful for prevention of arterial thrombosis in combination with thrombolytic therapy.
The listing or discussion of a prior-published document in this specification should not necessarily be taken as an acknowledgement that the document is part of the state of the art or is common general knowledge.
There remains a great need in the art for a low molecular weight peptide with procoagulant activity for treatment of patients with hemophilia A (FVIII deficiency). The present invention provides novel low molecular weight peptides with procoagulant activity which can be used for the non-intravenous treatment of hemophilia A. The present prevention also provides these novel peptides for the treatment of a deficiency in FV, FVII, FX and/or FXI.